Turbine vane system

ABSTRACT

A turbine vane, especially a turbine vane of the last stages, respectively includes a lower area which is radially and externally arranged, an upper area which is radially and internally arranged, and a radial cooling air channel extending between the upper area and the lower area. Cooling air can be introduced into the channel via an inlet in the lower area, and can be at least partially discharged via an outlet in the upper area. The cooling channel includes a radial inner channel through which the cooling air flows from the lower area to the upper area, and an outer channel which is adjacent to the inner channel on the circumferential side thereof. The outer channel communicates with the inner channel and includes an outlet which is arranged in the lower area. Part of the cooling air flows back in the direction of the lower area via the outer channel and emerges via the outlet.

This application is the national phase under 35 U.S.C. § 371 of PCTInternational Application No. PCT/EP01/09015 which has an Internationalfiling date of Aug. 3, 2001, which designated the United States ofAmerica and which claims priority on European Patent Application numberEP 00117667.6 filed Aug. 16, 2000, the entire contents of which arehereby incorporated herein by reference.

FIELD OF THE INVENTION

The invention generally relates to an arrangement of turbine guidevanes. In particular, it relates an arrangement including turbine guidevanes of the rearmost stages, in each case with a foot region arrangedradially on the outside, with a head region arranged radially on theinside and with a radial cooling-air duct which runs between the headregion and the foot region and into which cooling air can be introducedinto an inlet orifice in the foot region and can be at least partiallydischarged through an outlet orifice in the head region.

BACKGROUND OF THE INVENTION

A hot gas stream driving a turbine is conducted from the stationaryturbine guide vanes to the turbine moving blades which are fastened ondisks rotating about a central turbine axis. A circular arrangement ofturbine guide vanes, which are fastened with their radially outer footregions on a stationary turbine casing wall, in this case alternateswith an arrangement of turbine moving blades on a rotating disk. Theradially inner head regions of the turbine guide vanes are contiguous toa U-shaped inner ring which on its outside has a labyrinth seal whichseals off against a flow of hot gas around the U-ring.

Cooling air is used, as a rule, for cooling the turbine blades heated bythe hot gas flowing past. Where turbine guide vanes are concerned, thecooling air flows, for example through a radial cooling-air duct, formedin the turbine guide vane, from the radially outer foot region of theturbine guide vane as far as the radially inner head region. The coolingair is introduced from the head region into the contiguous U-shapedring. The latter is cooled by the cooling air flowing past. Moreover, anexcess pressure of the cooling air is intended to prevent hot gas frompenetrating into the cavity formed by the head region of the turbineguide vanes and by the U-shaped ring lying below them.

One problem, in this case, is that, for manufacturing and cost reasons,the U-shaped ring usually consists of a material of relatively lowtemperature resistance. When flowing through the turbine guide vane, thecooling air, as a rule, heats up to the maximum permissible temperatureof the turbine guide vane. Thus, when it flows into the U-ring, thecooling air which is already at a very high temperature may not providesufficient cooling of the U-ring in the case of small cooling-airquantities which would suffice for cooling the turbine guide vane of arear stage which is not very hot, as compared with the other turbineguide vane stages. This presents a problem also because the cooling airintroduced into the cavity formed by the U-ring and the turbine vanehead region, after flowing through the cavity, is discharged and flowsin the direction of the rearmost, largely uncooled heat-sensitiveturbine moving blade disk.

The solution adopted hitherto for solving the problem has been toconduct a large amount of cooling air through a central bore of theturbine guide vane or through a cooling-air duct of a largelyhollow-cast turbine guide vane.

SUMMARY OF THE INVENTION

An object of an embodiment of the present invention is, therefore, toprovide an arrangement of turbine guide vanes, which has a lowercooling-air requirement, at the same the U-shaped ring beingsufficiently cooled.

An object may be achieved in that the cooling-air duct has a radialinner duct, through which the cooling air flows from the foot region tothe head region, and an outer duct which is contiguous to the inner ductand which at least partially surrounds the inner duct circumferentially,communicates with the inner duct and has an outlet orifice in the footregion, a cooling-air fraction flowing through the outer duct back inthe direction of the foot region and flowing out through the outletorifice.

What is achieved by dividing the cooling-air duct into an inner duct andan outer duct is that the cooling air first flows through the inner ductand partially flows out at the foot region in order to cool the U-shapedring and partially, after being diverted, flows back through the outletduct again. The inner duct has the total cooling-air quantity flowingthrough it and has a smaller cooling-air quantity flowing around it inthe form of a counterflow. The cooling-air stream in the outer ductsurrounding the inner duct is in this case very rapid. It thereforeprovides good cooling of the surrounding regions of the turbine guidevane by virtue of the increased cooling capacity of a rapid cooling-airflow. The cooling air flowing back in a rapid stream, on the one hand,isolates the inner duct and makes it possible for the cooling air tohave a low temperature at the outflow point into the U-ring at the headregion, without large quantities of cooling air having to be used.

At the same time, the cooling air flowing back cools the side walls ofthe cooling-air duct and consequently the surrounding regions of theturbine guide vane which are the load-bearing regions of the turbineguide vane. According to an embodiment of the invention, the walls ofthe turbine vane which surround the cooling-air duct are made thickerthan in the prior art and are therefore more stable. Thus, by part ofthe cooling-air stream being diverted through the outer duct and by themore rapid conduction of the cooling air in the outer duct, the totalcooling-air quantity is reduced and, at the same time, the temperatureof the cooling air emerging from the turbine guide vane in the headregion in order to cool the U-ring is lowered.

An embodiment of the invention thus affords the advantage that both theturbine guide vane and the U-shaped ring are sufficiently cooled bysmall cooling-air quantities.

If the turbine guide vanes are turbine guide vanes of the rearmoststages, there is a relatively high saving in terms of cooling air, ascompared with the use of conventional cooling-air ducts, because the hotgas, by the time it reaches the last stages, has already beenappreciably cooled. Therefore the turbine guide vanes of the rearmoststages, in principle, are not heated up to such a great extent.Precisely for these turbine guide vanes, therefore, the arrangementaccording to the invention of the turbine guide vanes affords thepossibility of a substantial saving in terms of cooling air.

If the outer duct surrounds the inner duct circumferentially virtuallyon all sides, the heat radiation of the cooling air conducted throughthe inner duct is discharged, virtually on all sides, by the part of thecooling air which can be conducted through the outer duct. A high heattransmission is possible in a short time on account of the large radiantsurface. The cooling air arriving in the head region thus has a very lowtemperature and can optimally cool the U-shaped ring.

If the inner duct has at least one communication bore, through which thecooling air can flow over into the outer duct, the cooling air isaccelerated to a very great extent at the location of the bore. Thisimproves the cooling properties of the cooling air in the outer duct,since more heat can be absorbed due to the higher velocity.

A long cooling-air path within the turbine guide vane and therefore agood utilization of the cooling air are achieved if the inner duct hasat least one communication bore at a head-side end region. The coolingair can shield the cooling-air pipe, over virtually the entire lengthbetween the head and the foot region, from the hot vane wall, so thatthe cooling air emerging in the head region of the turbine guide vanehas, even in the case of a small cooling-air stream in the inner duct, asufficiently low temperature to cool the U-shaped ring effectively. Thecooling-air stream flowing back in the outer duct at the same time coolsthe surrounding regions of the turbine guide vane.

It is advantageous if the turbine guide vane has at the foot region, ina trailing edge region, an outlet orifice which is connected to theouter duct. Diverted cooling air which has brushed past the inner ductemerges from the turbine guide vane through the outlet orifice, withoutany intermixing with the introduced cooling air occurring. Thearrangement of the outlet orifice in the trailing edge region prevents apenetration of onflowing hot gas which would lead to damage. Since theoutlet orifices with the cooling air flowing through the outer duct areaccommodated in the foot region of the turbine guide vane, the coolingair has a very long path within the turbine guide vane and, even in thecase of relatively small cooling-air quantities, can absorb acorrespondingly large amount of heat energy from the turbine guide vaneand discharge it outward, without the air in the inner duct being heatedup.

If the inner duct is cylindrical, the velocity and nature of the flow ofthe cooling air flowing around along the entire duct length. Thereforealso the transporting away of heat, are approximately the same. Auniform cooling capacity is thereby ensured.

An advantageous embodiment of the invention is provided if the innerduct is a cooling-air guide pipe which can be inserted into thecooling-air duct and which is arranged at a distance from inner walls ofthe cooling-air duct, and if the outer duct is formed by the interspacebetween the cooling-air guide pipe and the inner walls of thecooling-air duct. The production of the cooling duct is simplified. Thecooling-air guide pipe can be inserted into the cooling-air duct aftercasting. The outer duct then consists of the interspace extending aroundthe cooling-air guide pipe. The thickness of the interspace, whichcorresponds to the distance of the cooling-air guide pipe from the sidewalls of the cooling-air duct, can be set, as required. The narrower theinterspace is, the higher the velocity of the forced-through cooling airbecomes.

An increase in cooling-air velocity in turn increases the ability of thelatter to transport away heat.

It is advantageous if the cross section of the outer duct is selectedsuch that the cooling air flows rapidly through the duct andconsequently sufficient cooling is ensured.

An object also relates to a method for producing a turbine guide vane.

An object may be achieved by a casting method for producing anarrangement of turbine guide vanes. The method employing a core whichgenerates the cooling-air duct of the turbine guide vane, the corehaving a smaller cross section than conventional cores for the castingof turbine guide vanes. A cooling-air guide pipe is provided with atleast one communication bore being inserted, after casting, into thecooling air duct at a distance from the inner walls of the cooling airduct. Further, outlet orifices which pass through as far as the outercontour of the turbine guide vane are introduced into the wall in thetrailing edge region of the foot region of the turbine guide vane.

During production, the form of the vane core for casting can be reducedin size, as compared with conventional casting cores. Since theresulting cooling duct is therefore smaller, the wall thickness of theturbine vane thus increases sharply, in particular, toward the inletedge. Casting is therefore appreciably simplified in terms of uncriticalwall thicknesses. After casting, a cooling-air guide pipe is theninserted. Between the cooling air guide pipe and the cooling-duct innerwall there is only a narrow outer duct which surrounds the cooling-airguide pipe annularly. By the reduction in size of the casting core andtherefore of the area of the cooling-duct inner wall, the radiantsurface for heat radiation and consequently the heat quantity dischargedper unit time into the cooling-air stream are reduced. The cooling airis therefore not heated up to such a great extent. A smaller cooling-airquantity is sufficient.

The cooling of the turbine guide vane is sufficient at the relativelylow temperatures, particularly in the rear stages.

BRIEF DESCRIPTION OF THE DRAWINGS

An exemplary embodiment of the invention will be given with reference tothe figures of which:

FIG. 1 shows a turbine guide vane of the rearmost stages,

FIG. 2 shows a longitudinal section through a turbine guide vaneaccording to FIG. 1, and

FIG. 3 shows a diagrammatic illustration of the temperature developmentof the cooling-air mass flows.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a perspective illustration of a turbine guide vane 1 of therearmost stages. With the aid of the foot region 2, which has holdingprojections 24, the turbine guide vane 1 is fastened to an inner wall,not illustrated, of a cylindrical turbine casing. The turbine guide vane1 extends from there with its vane leaf 18 radially in the direction ofa central turbine axis 30 of the turbine casing. The radially innertermination of the turbine guide vane 1 is formed by the head region 3which has a platform 25 and, with respect to the turbine axis 30, aradially inner arcuate recess 26. A U-shaped ring 19 is coupled to thishead region 3 by means of rail-like holding projections 27. The holdingprojections 27 in this case engage in holding grooves 28 of the U-shapedring 19.

The arcuate recess 26 of the head region 3 delimits, together with theU-shaped ring 19, a cavity 20, the longitudinal direction 29 of whichruns transversely to the turbine axis 30 and to a vane axis 31. Locatedon the U-shaped ring 19 radially on the inside is a labyrinth seal 21.The latter seals off against a direct throughflow of hot gas 17 theturbine moving blade disk 22 which, during the operation of the turbine,rotates about the central turbine axis 31 and lies contiguously belowsaid labyrinth seal and which is equipped with turbine moving blades,not illustrated.

The vane leaf 18 has a radial cylindrical cooling-air duct 4 which runscontinuously from an inlet orifice 36 of the cooling air 23 in the footregion 2 of the turbine guide vane 1 as far as its outlet orifice 35 ofthe cooling air in the head region 3 of the turbine guide vane 1. Thecooling-air duct has a cross-sectional contour 34 which, in the regionof the vane leaf 18 and of the foot region 2, resembles the outercontour 16 of the vane leaf 18. When viewed from the foot region 2, thecross-sectional contour 34 of the cooling-air duct 4 is essentiallymaintained in its form to just before the head region 3, but maydecrease in size. At the entry of the cooling-air duct 4 into the headregion 3, the cross section 34 narrows in the form of a continuous step33. This narrowed cross section 34 is then approximately maintained asfar as the recess 26 in the head region 3, in which recess lies theoutlet orifice 35 of the cooling duct 4 into the cavity 20.

A cylindrical cooling-air guide pipe 13 is inserted approximatelycentrally into the cooling-air duct 4. The cooling-air guide pipe 13 hasa virtually uniformly elliptic cross section 15. The cooling-air guidepipe 13 is held at the head region 3 of the turbine guide vane 1essentially in that it reaches as far as the continuous step 33 with across section 15 adapted to the transition or is even inserted in thehead region 3 into the narrowed cross section 34 of the cooling-air duct4. The cooling-air guide pipe 13 is held centrally in the foot region 2,for example, by means of spacer webs 37 mounted on side walls 8 of thecooling-air duct 4. The cooling-air duct 4 can be directly cast, duringthe casting of the turbine vane 1, by the insertion of a casting core.The cooling-air guide pipe 13 is inserted, after casting, into thecooling-air duct 4.

In the foot region 2, the cooling air 23 is introduced into the inletorifice 36 of the cooling-air guide pipe 13 which reaches as far as atop side 32 of the foot region 2 of the turbine guide vane 1.

The cooling air 23 then flows through the cooling-air guide pipe 13 asfar as a communication bore 10. One cooling-air stream fraction 42 flowsfurther on as far as the head region 3 of the turbine vane 1 and therethrough the outlet orifice 35 into the cavity 20. Another cooling-airstream fraction 41 flows from the cooling-air guide pipe 13 through acommunication bore 10 into an outlet duct 9 between the cooling-airguide pipe 13 and the cooling-air duct 4 and there, in the oppositedirection, toward the foot region 2, as illustrated in FIG. 2. By use ofthe narrowed bores 10, the cooling-air fraction 41 flows, accelerated,onto the cooling-duct inner wall 8. This gives rise, due to the smallerdiameter of the bore 10, to an acceleration of the cooling-air flow 41and therefore to a very pronounced cooling effect on the cooling-ductinner wall 8. Since the outer duct 9 is narrower than the cooling-airguide pipe 13, the cooling-air stream fraction 41 flows more rapidlythere.

Finally, the heated cooling air 41 is discharged through an outletorifice 12 which, at the trailing edge region 11 of the vane leaf 18,extends from the outer duct 9 to the vane outer contour 16 of theturbine guide vane 1. The cooling-air fraction 42 flowing out throughthe outlet orifice 35 in the head region 3 first flows into the cavity20 and cools the U-shaped ring 19 which delimits the cavity 20 radiallyon the inside. The cooling-air stream 42 can then emerge through a bore38 in a wall 40 of the U-shaped ring 19.

FIG. 2 shows a longitudinal section through the turbine guide vane 1according to FIG. 1. The entire cooling-air stream 23, which flows intothe cooling-air guide pipe 13 at the foot-side end region 5, is splitinto two cooling-air stream fractions. These include the deflectedcooling-air stream 41, which flows through the bores 10 at the head-sideend region 6 into the outer duct 9 and flows out again at the outletorifice 12, and the cooling-air stream 42 flowing out to the U-shapedring 19.

FIG. 3 shows the development of the temperature T of the cooling-airstream fractions 41, 42 while they flow through the turbine guide vane 1in the longitudinal direction 31 as far as an end length 1 of thecooling-air duct 4. The maximum temperature Tmax is not reached by thecontinuous stream 42, with the result that the U-shaped ring can besufficiently cooled. By contrast, the other cooling-air fraction 41absorbs the greater part of the heat and conveys it out of the turbinevane, without the heat being capable of damaging thetemperature-sensitive regions. The total cooling-air quantity 23, thesum of the two stream fractions 41, 42, is substantially lower than inthe prior art.

The invention being thus described, it will be obvious that the same maybe varied in many ways. Such variations are not to be regarded as adeparture from the spirit and scope of the invention, and all suchmodifications as would be obvious to one skilled in the art are intendedto be included within the scope of the following claims.

1. A turbine guide vane, comprising: a foot region, arranged radially onthe outside; a head region arranged radially on the inside; and acooling-air duct, running between the head region and the foot region,including, an inlet orifice in the foot region adapted to receivecooling air, an outlet orifice in the head region adapted to at leastpartially discharge air, a radial inner duct, through which the coolingair is adapted to flow from the foot region to the head region, and anouter duct, contiguous to the inner duct and at least partiallysurrounding the inner duct circumferentially, adapted to communicatewith the inner duct and including an outlet orifice in the foot region,wherein a cooling-air fraction is adapted to flow through the outer ductback in the direction of the foot region and is adapted to flow outthrough the outlet orifice.
 2. The turbine guide vane as claimed inclaim 1, wherein the outer duct virtually completely surrounds the innerduct circumferentially.
 3. The turbine guide vane as claimed in claim 2,wherein the inner duct includes at least one communication bore, throughwhich the cooling-air fraction is adapted to flow over into the outerduct.
 4. The turbine guide vane as claimed in claim 2, wherein thecommunication bore is arranged in head-side end region.
 5. The turbineguide vane as claimed in claim 2, wherein the turbine guide vaneincludes in the foot region, in a trailing edge region, an outletorifice adapted to communicate with the outer duct.
 6. The turbine guidevane as claimed in claim 2, wherein the inner duct is cylindrical. 7.The turbine guide vane as claimed in claim 2, wherein the inner duct isa cooling-air guide pipe, adapted to be inserted into the cooling-airduct and arranged at a distance from the inner wall of the cooling-airduct, and wherein the outer duct is formed by the interspace between thecooling-air guide pipe and the inner wall of the cooling-air duct. 8.The turbine guide vane as claimed in claim 7, wherein the distance issmaller than a cross section of the cooling-air guide pipe.
 9. Theturbine guide vane as claimed in claim 2, wherein the flow of thecooling-air fraction is relatively more rapid in the outer duct than inthe inner duct.
 10. The turbine guide vane as claimed in claim 1,wherein the inner duct includes at least one communication bore, throughwhich the cooling-air fraction is adapted to flow over into the outerduct.
 11. The turbine guide vane as claimed in claim 10, wherein thecommunication bore is arranged in head-side end region.
 12. The turbineguide vane as claimed in claim 1, wherein the turbine guide vaneincludes in the foot region, in a trailing edge region, an outletorifice adapted to communicate with the outer duct.
 13. The turbineguide vane as claimed in claim 1, wherein the inner duct is cylindrical.14. The turbine guide vane as claimed in claim 1, wherein the inner ductis a cooling-air guide pipe, adapted to be inserted into the cooling-airduct and arranged at a distance from the inner wall of the cooling-airduct, and wherein the outer duct is formed by the interspace between thecooling-air guide pipe and the inner wall of the cooling-air duct. 15.The turbine guide vane as claimed in claim 14, wherein the distance issmaller than a cross section of the cooling-air guide pipe.
 16. Theturbine guide vane as claimed in claim 1, wherein the flow of thecooling-air fraction is relatively more rapid in the outer duct than inthe inner duct.
 17. The turbine guide vane as claimed in claim 1,wherein the turbine guide vane is of the rearmost stages.
 18. A methodfor producing a turbine guide vane as claimed in claim
 1. 19. A castingmethod for producing a turbine guide vane, comprising: generating acooling-air duct of the turbine guide vane using a core; inserting acooling-air guide pipe provided with at least one communication bore,after casting, into the cooling-air duct at a distance from inner wallsof the cooling-air duct; and introducing outlet orifices, extendingtoward an outer contour of the turbine guide vane, into the inner wallsin a trailing edge region of a foot region for the turbine guide vane.20. A casting method for producing a turbine guide vane, comprising:generating a cooling-air duct of the turbine guide vane using a core;inserting a cooling-air guide pipe provided with at least onecommunication bore, after casting, into the cooling-air duct at adistance from inner walls of the cooling-air duct; and introducingoutlet orifices, extending as far as an outer contour of the turbineguide vane, into the inner walls in a trailing edge region of a footregion for the turbine guide vane; wherein the turbine guide vanefurther comprises, a foot region, arranged radially on the outside, ahead region arranged radially on the inside, and a cooling-air duct,running between the head region and the foot region, including an inletorifice in the foot region adapted to receive cooling air, an outletorifice in the head region adapted to at least partially discharge air,a radial inner duct, through which the cooling air is adapted to flowfrom the foot region to the head region, and an outer duct, contiguousto the inner duct and at least partially surrounding the inner ductcircumferentially, adapted to communicate with the inner duct andincluding an outlet orifice in the foot region, wherein a cooling-airfraction is adapted to flow through the outer duct back in the directionof the foot region and is adapted to flow out through the outletorifice.